Xylene is monocyclic aromatic compound with two methyl groups attached to the benzene ring. It exists in three isomeric forms: ortho, meta and para-xylene. Mostly, the individual isomers of xylene are separated and consumed in specific end-uses. Ortho-xylene is used primarily in the synthesis of phthalic acid, unsaturated polyester resins, alkyd resins; meta-xylene is key component for the synthesis of isophthalic acid and para-xylene is an important precursor to terephthalic acid and dimethyl terephthalate.
Usually, xylene is synthesized by the Friedel-Crafts alkylation reaction. However, alkylation catalysts such as AlCl3, HF and H2SO4 employed in the Friedel-Crafts alkylation reaction have found to be environmentally hazardous. Therefore, in recent years, molecular sieve catalyst such as zeolites and silico aluminophosphate have attracted attention as alkylation catalysts, typically, due to their higher acidic properties, potential for regeneration and easy of separation from the reaction mixture.
However, use of such acidic alkylation catalysts in alkylation of toluene produces mix-xylenes, containing predominantly meta-xylene and para-xylene with very minor amount of ortho-xylene. While, the alkylation of toluene in the presence of basic alkylation catalyst such as Na—X-zeolite, Na—Y-zeolite, Na-beta-zeolite Na-ZSM-5 zeolite, Cs—X zeolite, Ba zeolite, and Rb—X zeolite predominantly, produces ethyl benzene and styrene due to side chain alkylation reaction.
Therefore, there is need to develop a simple and economic process for the preparation of isomers of xylene, particularly ortho-xylene using the basic alkylation catalyst.